A flat sound without any depth gives the impression of coming from a plane situated next to the listener when heard from a certain distance. A sound with depth gives the more pleasant impression of coming from sound sources disposed in several depth planes with relation to the listener.
In the sound processing domain, the need to modify sound or original sound recordings in order to give the listener optimal listening comfort is known. Such is the case, for example, with sound from a film or audio support.
From document EP-A-1 017 249 is known a method designed for picking up sound, recording sound and reestablishing sound that reproduces the natural sensation of sound spaces. This method is implemented by means of sound pickup, recording and broadcasting equipment. In this method sound pickup is performed with two microphones simultaneously, respectively called right and left microphones. The set of microphones is displaced with relation to a sound source by varying the distance and the height of each microphone in a mainly differential manner with relation to the source. That is, one microphone is moved closer to the sound source when the other is moved farther away, and vice versa. This distance is managed in such a way that any one of the two sides of a virtual plane, that extends from one microphone to the other, is moved away from one microphone or the other. Therefore, the right microphone may become the left microphone. The two microphones may also simultaneously be moved closer and farther with relation to said source. This method, which may be described as acoustic-analog, allows a sensation of depth to be given to a well-defined type of sound: the sound for which sound pickup was performed by means of two microphones, and for the position and position variation of these two microphones at the time of sound pickup.
This method presents limits. Indeed, depending on the manner in which the microphones are moved during sound pickup, the recorded sound has a particular hue. This hue, also called color, may seem more or less agreeable or more or less effective considering the desired effects. Furthermore, this hue is not modifiable.
In addition, considering the nature of the method, a specific sound pickup must be performed for every new sound to be processed. This specific sound pickup means that as many pickups must be performed for new sounds as for new sounds to be processed, without guaranteeing the expected result. This last remark means that a buyer cannot have unprocessed sound and processed sound simultaneously unless he has purchased an unprocessed version and a processed version. Furthermore, the buyer cannot pass simply from one version of the sound to the other by activating or not activating the transformation by using a control button unless he has a dual reader.
In the invention, a stereophonic sound signal is preferably used, but a monophonic sound signal may be used. From a conventional left right sound, the method produces a sensation of depth that transposes the listener into a three-dimensional space. The invention finds applications that are particularly advantageous, but not exclusive, in the processing of original audiotape for film. However, the invention may relate to the processing of any music audiotape, whether the latter is, in addition, stored on a tape backing or on a disk. The invention is designed for, among others, sound engineers who can, from a conventional sound signal without depth that is available on a commercial support, apply transformations in such a way as to give volume and the desired enveloping to the sound. The invention also relates to industrial applications that consist of installing elements, for example memories, that incorporate the parameters that are necessary and sufficient for implementing sound processing according to the invention on large public machinery. Like the sound engineer, the end user may give the sound the desired depth at the desired time by using his stereo system, television or digital music reader controls.